This invention relates to a method and product aspects of spin forming an end portion of a cylindrical sheet metal workpiece to form a radial flange section and a double-thickness rim at the periphery of the radial flange section.
At least as early as the 1980""s Spiral Fittings, Inc., presently located in Andrews, S.C., has spun formed cylindrical workpieces to make connector rings for cylindrical HVAC ducting. The Spiral Fittings"" connector ring is formed by spin forming a cylindrical workpiece to provide a radial flange at one of its ends. The radial flange becomes what is known as a xe2x80x9cmating flangexe2x80x9d and the unworked portion of the workpiece becomes what is known as an xe2x80x9cinsertion flange.xe2x80x9d This structure is used as a connector ring at one end of a section of HVAC ducting. The insertion flanges of two such connector rings are inserted into end portions of two sections of ducting that are to be connected together. Sheet metal screws or the like are used to connect the end portions of the sections of ducting to the insertion flanges of two connector rings. Then, the two sections of ducting are put into axial alignment with their mating flanges moved almost together. An annular seal is placed between the two mating flanges and nuts and bolts are used to connect the mating flanges together with the sealing ring held between them. A disadvantage of the Spiral Fittings"" connector ring is that the mating flanges are relatively flexible and have sharp edges at their outer peripheries.
It is known to provide connector rings for oval ducts with mating flanges having outer peripheries that are in various ways made to be blunt instead of sharp. Example connector member profiles are disclosed by U.S. Pat. No. 5,129,690, granted Jul. 14, 1992 to Manfred Meinig, Peter J. Arnoldt and Fredrick J. Arnoldt. The SMACNA HVAC Duct Construction Standards include several types of standard connector profiles for HVAC ducting. One of these profiles is the T-23 profile which has a double-thick radial flange. Another standard profile is the T-24 profile. It has a cylindrical return hem section at the periphery of the radial flange.
U.S. Pat. No. 5,983,496 granted Nov. 16, 1999 to Jeffrey Allen Hermanson discloses spin forming a cylindrical sheet metal workpiece to make a connector ring for HVAC ducting. Like Spiral Fittings, Inc., Hermanson spin forms a cylindrical workpiece to form a radial flange at one end of the workpiece. The unaltered portion of the workpiece becomes an insertion flange and the radial flange becomes a mating flange. Whereas Spiral Fittings, Inc. leaves a sharp edge at the periphery of its mating flange, Hermanson continues the spin forming operation to form a cylindrical return hem section at the periphery of the mating flange and give the connector ring a standard SMACNA T24 profile.
The method of the present invention also continues the spin forming process but uses different action steps and tooling to form a modified T-23 profile at the periphery of the mating flange in place of Hermansonas cylindrical, T-24 return hem section.
The invention includes an improved method of spin forming a cylindrical sheet metal workpiece, to form a sheet metal connector ring or sheet metal ducting. A mandrel is used that has an open center, a generally radial forming surface surrounding the open center, and an outer diameter. A first end portion of the workpiece is positioned in the open center of the mandrel and is secured to the mandrel. A second end portion of the workpiece projects axially outwardly from the center opening in the mandrel and has an outer end part. The mandrel and the workpiece are spun together about a common spin axis and during spinning the second end portion of the workpiece is progressively stretched in diameter and moved radially outwardly on to and along the generally radial forming surface of the mandrel. The mandrel and workpiece are rotated and a first forming tool is used to stretch the second end portion of the workpiece and move it radially outwardly, on the radial forming surface. This is done at least until the outer end part of the second end portion of the workpiece becomes spaced generally axially from the radial forming surface substantially at the outer diameter of the mandrel. Accordingly to one aspect of the invention, the rotation of the mandrel and workpiece is continued and a second forming tool is moved against the outer end part of the second end portion of the workpiece. This second forming tool is used to fold the outer end part radially inwardly and move it substantially against an adjoining radial part of the second end portion of the workpiece that is in contact with the radial forming surface on the mandrel. Preferably, a forming tool is used to press the outer end part of the second end portion of the workpiece flat against the adjoining radial part of the second end portion of the workpiece. Following these forming steps, the formed workpiece is removed from the mandrel to become a connector ring that has a radial flange at a first end and a cylindrical flange at a second end, wherein the radial flange has an outer marginal portion with a rounded outer edge.
The method includes providing a first forming tool that includes a roller having a center axis. The roller is mounted for free rotation about the center axis. The roller is provided with a convex face. The roller is positioned inside the second end portion of the workpiece, with its convex face directed towards the second end portion of the workpiece. The roller is then moved along a path that is within a plane that includes the spin axis of the mandrel and the center axis of the roller. As it moves, the roller progressively stretches the second end portion of the workpiece and progressively forces it against the generally radial forming surface of the mandrel.
The invention further includes providing a support arm for the first forming tool. The support arm is pivotally connected at a lower end to a support frame, for pivotal movement about a pivot axis that extends perpendicular to the center axis of the roller. The roller is mounted onto the support arm at a location spaced from the pivot axis. The support arm is swung about the pivot axis to place the roller inside of the second end portion of the workpiece, in position to contact the second end portion of the workpiece and stretch it and force it against the radial forming surface of the mandrel as the roller is being moved. In preferred form, the mandrel is mounted to rotate about a spin axis that extends substantially vertically. As a result, the generally radial forming surface is in a plane that extends substantially horizontally.
The invention includes mounting the first forming tool for movement towards and away from the generally radial forming surface of the mandrel, and spring biasing the roller towards the radial forming surface. As a result, when the first forming roller is moved to stretch the second end portion of the workpiece and force it against the generally radial forming surface of the mandrel, the first forming roller will be urged by its contact with the workpiece and caused to move upwardly against its bias so as to provide space between its periphery and the radial forming surface of the mandrel for the workpiece material that is being moved radially outwardly in contact with the radial forming surface of the mandrel.
The present invention also includes providing a second forming tool that includes a roller that has a center axis and a cam surface that surrounds the center axis. The second forming tool is moved radially to place its cam surface against the outer part of the second end portion of the workpiece. It is further moved to cause the cam surface to cam the outer part of the second end portion of the workpiece both radially inwardly and axially towards an adjoining radial part of the second end portion of the workpiece that is in contact with the radial forming surface on the mandrel.
A third forming tool may be provided for pushing down on the folded back portion of the mating flange, so as to push it tight against the adjoining portion of the mating flange that is below it.
The present invention includes providing a connector ring having a cylindrical insertion flange sized to be received within an end portion of a section of sheet metal ducting. It also includes a radial mating flange extending radially outwardly from one end of the insertion flange to an outer edge. The mating flange has an annular, single-thickness, inner portion and an annular, double-thickness, outer portion. The inner portion extends radially outwardly from one end of the insertion flange and then makes a jog. One thickness of the outer portions extends radially outwardly from the jog. The other thickness of the outer portion extends radially inwardly along one side of the first thickness, substantially coplanar with the inner portion of the mating flange. The double-thickness outer portion has a laterally rounded outer edge and an inner edge that is spaced radially inwardly from the outer edge on the side of the mating flange that is opposite the insertion flange. The inner edge forms an inner boundary for the double-thickness, outer portion of the mating flange.
The present invention further includes providing a connection between adjoining ends of two duct sections. Two sheet metal connector rings of the type described above are provided, one for each duct section. The cylindrical insertion flange of each connector ring is telescopically received in the end portion of its section of sheet metal ducting. The radial mating flanges of the two connector rings confront each other with their double-thickness outer portions confronting each other. An axial space is formed between the mating flanges. A seal ring is situated in the space, contacting the mating flanges. Fasteners (e.g. sheet metal screws) connect the end portions of the duct sections to the insertion flanges of the connector rings. Fasteners (e.g. sheet metal screws) connect the mating flanges of the two connector rings together.
Other objects, advantages and features of the invention will become apparent from the description of the best mode set forth below, from the drawings, from the claims and from the principles that are embodied in the specific structures that are illustrated and described.